Ziegler-Natta catalyst systems are well known for their capability to polymerize olefins. They in general consist of a support which mostly is magnesium based onto which titanium component has been added along with organic compound known as internal donor. This catalyst when combined with co-catalyst and/or external donor comprise of the complete ZN catalyst system. Various internal donors are incorporated during catalyst synthesis to enhance specific properties of the polyethylene catalyst. Internal donors like tetrahydrofuran, ethyl benzoate, tetraethoxysilane, dimethylformamide etc are well known commercially used in polyethylene catalyst.
U.S. Pat. No. 4,859,749 describes two-stage polymerization process using a modified supported catalyst for ethylene polymers. The supported catalyst used is formed by reaction of a magnesium alcoholate with a titanium-IV compound in suspension and subsequent reaction with a halogen-containing organoaluminum compound and activation of the solid thus obtained by an aluminum trialkyl or aluminum isoprenyl. This catalyst has the disadvantage of generating higher amount of undesirable side products which act as either poison and hence lowers the catalyst activity or generate low molecular weight polyethylene which leads to fouling.
U.S. Pat. No. 5,260,245 describes a catalyst for producing higher flow index linear low density polyethylene with relatively narrower molecular weight distributions using catalyst which is formed by treating silica having reactive OH groups with a dialkylmagnesium in a solvent. Then adding to said solvent a carbonyl containing compound to form an intermediate which is subsequently treated with a transition metal to form a catalyst precursor. The catalyst precursor is activated with triethylaluminum. This invention relates to the in-situ generation of internal donor due to the addition of carbonyl compound.
CN 104974283 describes the catalyst component obtained by loading magnesium/titanium-containing solid with at least one inorganic titanium compound, at least one organic titanium compound, at least one electron donor compound and at least one activator. The magnesium titanium-containing solid is prepared by the following method: dissolving magnesium compound in a solvent system comprising organic epoxy compound and organophosphorus compound to form a homogeneous solution, and co-precititating with titanium compound and one or more organic ester compound in the presence of composite co-precipitant. The catalyst component has relatively narrow particle size distribution and small ay. particle size. The catalyst has high activity and high hydrogen response, and can get polymer with low fines content. This invention also describes the usage of organic ester as internal donor to improve catalyst property.
U.S. Pat. No. 6,803,338 describes the solid titanium catalyst used for homo- and co-polymerization of ethylene, having excellent in catalytic activity and producing polymers with a high bulk density and less polymer soluble in the medium. The solid titanium catalyst is produced by Step (i) producing a magnesium solution by contact-reacting a halogenated magnesium compound and alcohol, Step (ii) reacting the solution with a phosphorus compound and an ester compound having at least one hydroxy group, and Step (iii) adding thereto a mixture of a titanium compound and a silicon compound.
Hence, there is always a need of better catalyst as well as polymerization processes which give better performance in cost effective manner.